The Swiss federal energy office, Bundesamt für Energie (BfE), has concluded that using wind energy to replace output from Swiss nuclear power stations "seems technically possible at an economically acceptable cost." Studies by research institutes Prognos in Basle and Infras in Zurich, conducted on behalf of the BfE, both concluded that electricity generation from Swiss reactors could be replaced with wind energy imported from neighbouring European countries. If a strategy to import wind energy is adopted it would need to be backed by state driven measures such as an international trade in green certificates with obligatory quotas, the BfE adds. Both studies comment that lack of experience with offshore wind energy is a concern, while the availability and costs of additional reserve capacity to back up wind generation should be investigated. The Prognos study suggests 1200 MW of reserve capacity will be needed in 2020 and 3000 MW by 2030 because closing reactors and ending nuclear import will leave a supply gap of 10 TWh in 2020 rising to 25.6 TWh by 2030.